On Christmas Day this year, astronomers and space enthusiasts around the world will be celebrating the third anniversary of the launch of the James Webb Space Telescope, which sailed into orbit aboard an Ariane 5 rocket (from the Guiana Space Centre in South America) before making its way out to a distance of some 930,000 miles from the Earth—almost four times farther away than the Moon. It took about a month to reach its station, a ‘gravitational dead zone’ known as L2, where it enjoys continuous, uninterrupted views of the Universe. Its instruments, designed to operate at exceptionally low temperatures, are protected from the intense light and heat of our star by a tennis-court-sized sunshield comprising five layers of ultra-thin Kapton. After several more months of deployment and testing, Webb was ready to return its first images, and in July 2022 they were finally revealed to the world.
Credit: NASA, ESA, CSA, STScI
Since that momentous press conference, Webb has continued to the pull back the veil of an unknown universe, and produce images that never fail to dazzle us and make headlines. But how does it go beyond previous missions, and why was it designed this way? At Webb’s technological heart is its enormous, eye-catching golden mirror. Comprising eighteen hexagonal segments, it spans six and a half metres and collects an astonishing amount of light to be focussed onto Webb’s detectors. For comparison, the main mirror in the Hubble Space Telescope is just under two and a half metres wide.
Credit: NASA/Chris Gunn
Webb’s giant mirror is just one component of its next-generation design. It doesn’t only see fainter and finer details than Hubble, it sees them in a whole new light. Some consider Webb to be a successor to Hubble, but it’s more correct to see it as a complementary tool—a sibling observatory that will scrutinise the same objects from a unique perspective. Hubble performs its observations in ‘optical’ wavelengths, what astronomers call the visible part of the spectrum. Webb on the other hand, looks far outside the visible spectrum to detect infrared light. We don’t see this radiation, but we do feel some of it in the form of heat. We also emit it, as do stars and other cosmic sources.
Credit: NASA, ESA, CSA, STScI, J. DePasquale, A. Koekemoer, A. Pagan (STScI), ESA/Hubble and the Hubble Heritage Team
The difference is evident when comparing side-by-side images from both observatories. Looking at the famous ‘Pillars of Creation’ in the Eagle Nebula, we can see how Webb (right) is able to peer through dense clouds of dust and gas that obscure Hubble’s (left) view. Within these clouds, infant stars are beginning to shine, sculpting intricate structures in the gas around them, which astronomers can use to decipher the processes that govern the evolution of the nebula.
Credit: NASA, ESA, CSA, STScI, J. DePasquale, A. Koekemoer, A. Pagan (STScI), ESA/Hubble and the Hubble Heritage Team
It’s like performing an x-ray, but Webb is using infrared light. This is collected by the detectors in its instruments, the two most famous of which are the cameras that make such gorgeous images possible. NIRCam (Near Infrared Camera) and MIRI (Mid-Infrared Instrument) are both precision-made to deliver sharp views at a wide range of wavelengths. They can be operated through a bewildering array of filters, and as such vibrant, multichannel images become possible. Of course, none of this light is visible to the eye at all, so astronomers will typically use three or more different filters, and assign them to visible colours. How those colours are chosen is up to the person doing the image processing, so there’s a human perspective too. It’s an intersection of art and science at work.
Credit: NASA, STScI, Tom Kerss
NIRCam and MIRI are two of five instruments that detect the infrared light focussed by Webb’s mirrors. Alongside them are two spectrographs, which provide even more information for astronomers. Often, it is a combination of these instruments that delivers the deepest insights, but each is individually a cutting-edge piece of equipment, capable to cementing Webb as the most powerful space-based observatory ever built.
An early success for Webb came in 2023, when it identified what is believed to be some of the most distant galaxies ever observed. Using NIRCam, astronomers discovered galaxies from as early as 300 million years after the Big Bang, a time known as the Epoch of Reionization. During this period, the first stars and galaxies were forming, ending the cosmic "dark ages." In addition to its work on the distant Universe, Webb is also making remarkable discoveries closer to home. Within the Milky Way, it is very capable of studying exoplanets—planets outside our Solar System—and analysing their atmospheres. With its suite of instruments, Webb can detect the infrared signatures of the molecules that make up these atmospheres, providing clues about their composition, temperature, and even the possibility of habitability.
As these remarkable advances in understand progress, Webb will continue to deliver visions of the Universe that exceed expectations and delight all of us here on Earth. In my book, Unknown Universe, I’ve collected images from the first years of the mission and provided my own insight into what we’re seeing. You can pick up a copy from wherever you buy your books and celebrate this new era of astronomy as Webb prepares to enter its fourth year in space.
About the author
Tom Kerss is an astronomer, astrophotographer, writer and speaker, specialising in the rewarding task of connecting people to their shared universe. He is the author of Unknown Universe, which will be released on October 10th 2024.